How It Works - The Science of Smell and Taste
Our combined senses of smell & taste are called the chemical senses because they sense and interpret the biochemistry of life. These senses direct us away from danger, help us identify the world around us, and attract us toward what is pleasant. Smell smoke and instinctively you run away. Catch a whiff in your garden and you immediately know a rose from a pine tree. A whiff of perfume or cologne may attract you to your future mate.
These senses are tied to a complex messenger system connecting your brain, nervous system, and digestive processes. This natural bio-sensory process stimulates emotional responses that direct our actions, evokes memories, and can calm or excite us. We feel these emotions in our head, our heart, and ‘gut.’
In the search for nutrients and foods our highly evolved senses of smell & taste have two big tasks – keep us safe from ingesting dangerous or inappropriate foods or substances and direct us to the foods and nutrients our bodies need for nourishment.
The Chemo Sensing combo of smell & taste are the gatekeepers of nutritional wisdom in both humans and animals. Think about it – in animals, and humans, the nose is located above the mouth. The design is to smell first, open mouth second. Animals instinctively sniff before eating. Chefs, wine stewards and coffee baristas have trained their senses of smell and taste to make food selection both pleasurable and nutritious.
By the way…what we call taste is actually flavor and nearly 80% of what we call flavor comes from smells. So when we talk about how smells are interpreted, just remember taste interpretation works the same way. However, something that passes our sniff test can fail the taste test – our second line of defense before we ingest anything.
While we all recognize that smell and taste can protect us from harm, you may wonder if these senses can really guide us to the nutrients and foods we need for nourishment. How smells are gathered and interpreted by our nose and brain is the first step in understanding the nose-to-need feedback loop. Inside our nose, beyond a finger’s reach lies a small mucus covered organ called the Olfactory Epithelium. This little organ captures a smell molecule in multiple and diverse receptor cells. In humans, these tiny hair-like receptors can recognize thousands of different smells. And while animals have more receptor cells, giving them a sharper sense of smell, they process smells in much the same manner as we do.
Once gathered by the nose, smell molecules are converted into chemical signals and passed on to the Olfactory Bulb. The Olfactory Bulb receives the information from the receptors in the form of neuro-transmitters and passes it along to the Olfactory Cortex.
The major centers of the brain run inventory checks through the brain, stomach and body via the Autonomic Nervous System (ANS) to identify and assign a preference or value to the smell. If the smell is dangerous, we get a strong feeling to move away from the smell. If the smell is pleasant, we’re motivated to move closer. Instinctively! It is not just our intellect at work here- it is our whole body responding over and above our intellect to get us moving in the appropriate, healthful direction.
Surprisingly, more than half of your smartest nerve cells are located in your digestive system. The “brains in your gut” contains neurons and neurotransmitters just like those found in your head. Just like your brain, your “gut brain” can learn, remember, and produce emotions. These emotions ‘flavor’ your perception of a smell or a taste. You either like it or you don’t.
The Autonomic Nervous System (ANS), which monitors and directs salivation and digestion (among many other tasks), opens up or shuts down digestion depending on this ‘like it or not like it’ response:
If your ‘gut – brain’ communication produces a pleasant smell or taste in response to a nutrient or food, digestion will be stimulated.
If you get an unpleasant smell or taste, your digestion will shut down.
Our body manages our constantly changing relationship to nutrients by modifying our smell & taste preferences. Our preferences and perception change according to the body’s demand for that nutrient.
Smell responses appear to be ‘subjective’ but the body is actually assessing its relationship to that nutrient and determining if it wants more or less. Hence our change in preference.
Research has shown when deficient in a specific nutrient, our Olfactory Cortex (OC) turns ups the sensitivity of receptors in the nose and taste buds. Meanwhile the brain-to-gut preference dialogue makes that nutrient stand out more clearly and smell better than ones not in demand. Once needs are satisfied, the OC resets itself, redirecting our preferences toward the next important nutrient on our body’s shopping list.
In research language if animals or humans are deficient or depleted in a nutrient, they have an appetite or hunger for that nutrient. When they are replete, or have reached satiety, they are satisfied and not hungry for that nutrient.
Smell & taste responses mirror our body’s changing needs while constantly monitoring and updating our nutrient preferences according to diet, activity and stress.
This on-going nutritional dialogue happens below our conscious awareness. While very complex in both the physiology and perceptual mechanics, the result is our body’s evolutionary way of guiding nutrient selection.
Scientists routinely conduct studies to see if animals can select the appropriate missing nutrients from a nutrient line-up. Not surprisingly, animals regularly and efficiently locate and satisfy their appetite for depleted nutrients.
In the lab, this is known as preference testing and is the basis of Smell and Taste Preference Tests. Preference testing measures smell & taste responses and is used to develop and market consumer products ranging from coffee drinks to perfumes. Preference basically means choosing or ranking what you like from a selection of smells or tastes.
Smell and Taste Preference Tests make it easy to rate smell & taste preferences for nutrients. Smell n Score & Taste n’ Score supplements are specifically formulated for smell or taste Preference Testing. A ‘Pleasant’ response indicates ‘take it’; an ‘Unpleasant or Bad’ response indicates ‘don’t take it.’ A neutral or no taste/smell response would indicate less appetite or hunger for than nutrient so the choice to take is up to the you.
Diet, activities, illness, injury, and stress affect your appetite for nutrients and foods. Your Preference responses or scores will reflect those changes daily, weekly, and monthly. Regular testing helps you keep up with your bodies changing demands.
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We invite you to go deeper into the science of smell and taste with our ever growing list of studies, books, articles and websites.
PHYSIOLOGY OF SMELL & TASTE
1] The rules of formation of the olfactory representations found in the orbitofrontal cortex olfactory areas in primates. Rolls ET. Chem Senses. 2001 Jun;26(5):595-604. Review.PMID: 11418505
2] Taste-olfactory convergence, and the representation of the pleasantness of flavour, in the human brain.de Araujo IE, Rolls ET, Kringelbach ML, McGlone F, Phillips N. Eur J Neurosci. 2003 Oct;18(7):2059-68.PMID: 14622239
3] Autonomic nervous system responses to odours: the role of pleasantness… Bensafi M et al. Chem Senses, 2002. 12379594
4] Autonomic nervous system responses associated with primary tastes. Rousmans S, Robin O, Dittmar A, Vernet-Maury E. Chem Senses. 2000 Dec;25(6):709-18.PMID: 11114149
5] The Physiology of Perception Freeman, W S, Sci Am 1991 Feb (264) 78-85. PMID: 2000483 The brain transforms sensory messages into conscious perceptions almost instantly Chaotic, collective activity involving millions of neurons seems essential for such rapid recognition.
6] Taste as a factor in the management of nutrition.Scott TR, Verhagen JV. Nutrition. 2000 Oct;16(10):874-85. Review.PMID: 11054592
7] Taste in the monkey cortex. Scott TR, Plata-Salamán CR. Physiol Behav. 1999 Oct;67(4):489-511. Review.PMID: 10549886
8] Taste responses in the nucleus tractus solitarius of sodium-deprived rats. Jacobs KM, Mark GP, Scott TR. J Physiol. 1988 Dec;406:393-410.PMID: 3254418
STUDIES RELATED TO SMELL & TASTE NUTRIENT SELECTION
1] Zinc taste test in pregnant women and its correlation with serum zinc level. Garg HK, Singal KC, Arshad Z. Indian J Physiol Pharmacol. 1993 Oct;37(4):318-22.PMID: 8112809
2] Calcium: taste, intake, and appetite. Tordoff MG. Physiol Rev. 2001 Oct;81(4):1567-97. Review.PMID: 115814973
3] Calcium deficiency alters chorda tympani nerve responses to oral calcium chloride. Inoue M, Tordoff MG. Physiol Behav. 1998 Jan;63(2):297-303.PMID: 9423972
4] Calcium deprivation increases the palatability of calcium solutions in rats. McCaughey SA, Forestell CA, Tordoff MG. Physiol Behav. 2005 Feb 15;84(2):335-42.PMID: 15708786
5] Voluntary intake of calcium and other minerals by rats. Tordoff MG. Am J Physiol, 1994. PMID:8067456
6] Latent learning about calcium and sodium. Coldwell SE et al. Am J Physiol, 1993. PMID:8285293
7] Response to NaCl taste in mixture with sucrose by sodium deficient rat… McCutcheon B et al. Physiol Behav, 1983. PMID:6867136
8] Ontogeny of the ionic specificity of sodium appetite in the rat pup. Leshem M et al. Dev Psychobiol, 1994. PMID: 8001727
9] Activity in rat nucleus tractus solitarius after recovery from sodium deprivation. McCaughey SA, Giza BK, Scott TR. Physiol Behav. 1996 Aug;60(2):501-6.PMID: 8840912
10] Magnesium appetite in the rat. McCaughey SA, Tordoff MG. Appetite. 2002 Feb;38(1):29-38.PMID: 11883915
11] Iron appetite and latent learning in rats. Woods SC, Vasselli JR, Milam KM. Physiol Behav. 1977 Nov;19(5):623-6.PMID: 616294
Monell Center: Advancing Discovery in Taste and Smell http://www.monell.org/